In communication systems having a communication transmission path between a communication source and a communication sink, transmitting and receiving devices are used for communication processing and transmission in which
1) the communication processing and communication transmission can take place in a preferred transmission direction (simplex operation) or in both transmission directions (duplex operation),
2) the communication processing is analogue or digital,
3) the communication transmission via the long-distance transmission path takes place wire-free on the basis of various communication transmission methods FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and/or CDMA (Code Division Multiple Access) for example in accordance with radio standards such as DECT, GSM, WACS or PACS, 1S-54, PHS, PDC etc. (see IEEE Communications Magazine, January 1995, pages 50 to 57; D. D. Falconer et al: xe2x80x9cTime Division Multiple Access Methods for Wireless Personal Communicationsxe2x80x9d) and/or by wire.
xe2x80x9cCommunicationxe2x80x9d is a generic term which covers both the message content (information) and the physical representation (signal). Despite a communication having the same message contentxe2x80x94that is to say the same informationxe2x80x94different signal forms may occur. Thus, for example, a communication relating to an item may be transmitted in any of the following forms
(1) an image,
(2) as the spoken word,
(3) as the written word,
(4) as an encrypted word or image.
The type of transmission according to forms (1), (2) and (3) is in this case normally characterized by continuous (analogue) signals, while the type of transmission according to forms (4) normally takes place by means of discontinuous signals (for example pulses, digital signals).
On the basis of this general definition of a communication system, the invention relates to a base station having a fast channel changing function in a cellular TDMA/FDMA radio system, in particular in a cellular DECT system.
A cellular radio system, as a subset of the previously defined communication system is, for example, the cellular DECT-System (Digital Enhanced (previously: European) Cordless Telecommunication; see (1): Nachrichtentechnik Elektronik 42 (Electronic telecommunication 42) (1992) January/February No. 1, Berlin, DE: U. Pilger xe2x80x9cStruktur des DECT-Standardsxe2x80x9d (Structure of the DECT Standard), pages 23 to 29 in conjunction with the ETSI Publication ETS 300175-1 . . . 9, October 1992; (2): Telcom Report 16 (1993), No. 1, J. H. Koch: xe2x80x9cDigitaler Komfort fxc3xcr schnurlose Telekommunikationxe2x80x94DECT-Standard erxc3x6ffnet neue Nutzungsgebietexe2x80x9d (Digital convenience for cordless telecommunicationsxe2x80x94DECT Standard opens up new application areas), pages 26 and 27; (3): tec 2/93xe2x80x94the Technical Magazine from Ascom xe2x80x9cWege zur universellen mobilen Telekommunikationxe2x80x9d (Universal mobile telecommunication techniques), pages 35 to 42; (4): Philips Telecommunication Review, Vol. 49, No. 3, September 1991, R. J. Mulder: xe2x80x9cDECT, a universal cordless access systemxe2x80x9d; (5): WO 93/21719 (FIGS. 1 to 3 with associated description)) or the cellular GAP-System (Generic Access Profile; ETSI-Publikation prETS 300444, April 1995, Final Draft, ETSI, FR), which may be designed, for example, on the basis of a monocellular DECT/GAP system (Single Cell System) according to FIG. 1 and in accordance with the illustration in FIGS. 4 and 5.
According to the DECT/GAP Standard and in accordance with the illustration in FIG. 1, a DECT/GAP radio interface which is designed for the frequency band between 1.88 and 1.90 GHz can be used to set up on a DECT/GAP base station BS a maximm of 12 links, using the TDMA/FDMA/TDD method (Time Division Multiple Access/Frequency Division Multiple Access/Time Division Duplex) in parallel with DECT/GAP mobile parts MT1 . . . MT12. The figure of 12 results from a number xe2x80x9ckgxe2x80x9d of time slots or telecommunications channels available for duplex operation of a DECT/GAP system (k=12). The links may in this case be internal and/or external. In the case of an internal link, two mobile parts which are registered at the base station BS, for example the mobile part MT2 and the mobile part MT3, can communicate with one another. In order to set up an external link, the base station BS is connected to a telecommunications network TKN, e.g. in cable form via a telecommunications line unit TAE, or a private branch exchange is connected to a cable telecommunications network, or (according to PCT Reference WO 95/05040 in wire-free form as a repeater station) to a higher-level telecommunications network. In the case of the external link, it is possible to communicate with a mobile part, for example with a mobile part MT1, via the base station BS and the telecommunications line unit TAE, or for the private branch exchange NStA to communicate with a subscriber in the telecommunications network TKN. Ifxe2x80x94as in the case of Gigaset 951 (Siemens cordless telephone, see Telcom Report 16, (1993) Issue 1, pages 26 and 27)xe2x80x94the base station BS has only one connection to the telecommunications line unit TAE or to the private branch exchange NStA, then only one external link can be set up. Ifxe2x80x94as in the case of Gigaset 952 (Siemens cordless telephone; see Telcom Report 16, (1993), Issue 1, pages 26 and 27)xe2x80x94the base station BS has two connections to the telecommunications network TKN then, in addition to the external link to the mobile part MT1, a further external link is possible from a cable telecommunications terminal TKE connected to the base station BS. In this case it is also in principle feasible for a second mobile part, for example the mobile part MT12, to use the second connection for an external link, instead of the telecommunications terminal TKE. While the mobile parts MT1 . . . MT12 are operated using a battery or a rechargeable battery, the base station BS, which is designed as a small cordless exchange, is connected to a voltage network SPN via a network interface unit NAG.
Based on the document Components 31 (1993), Issue 6, pages 215 to 218; S. Althammer, D. Brxc3xcckmann: xe2x80x9cHochoptimierte IC""s fxc3xcr DECT-Schnurlostelefonexe2x80x9d (Highly optimized ICs for DECT cordless telephones), FIG. 2 shows the basic circuit design of the base station BS and of the mobile part MT according to FIG. 1. According to this figure, the base station BS and the mobile part MT have a radio part FKT with an antenna ANT used for transmitting and receiving radio signals, a signal processing device SVE and a central controller ZST, which are connected to one another in the illustrated manner. The radio part FKT essentially contains the known devices such as the transmitter SE, the receiver EM and the synthesizer SYN. The signal processing device SVE contains, inter alia, a coding/decoding device CODEC. Both for the base station BS and for the mobile part MT, the central controller ZST has a microprocessor xcexcP with a program module PGM designed in accordance with the OSI/ISO layer model (see (1): Instruction Sheetsxe2x80x94Deutsche Telekom, Year 48, 2/1995, pages 102 to 111; (2): ETSI Publication ETS 300175-1 . . . 9, October 1992), a signal control section SST and a digital signal processor DSP, which are connected to one another in the illustrated manner. Of the layers defined in the layer model, only the first four layers, which are absolutely essential for the base station BS and for the mobile part MTxcex are illustrated. The signal control section SST in the base station BS is designed as a Time Switch Controller TSC, and that in the mobile part MT is designed as a Burst Mode Controller BMC. The major difference between the two signal control sections TSC, BMC is that the base-station-specific signal control section TSC also carries out switching functions that the mobile-part-specific signal control section BMC does not.
The basic method of operation of the circuit units mentioned above is described, for example, in the document cited above, Components 31 (1993), Issue 6, pages 215 to 218.
The circuit layout described according to FIG. 2 is supplemented by additional functional units in the base station BS and in the mobile part MT in accordance with their function in the DECT/GAP system according to FIG. 1.
The base station BS is connected to the telecommunications network TKN via the signal processing device SVE and the telecommunications line unit TAE or the private branch exchange NStA. As an option, the base station BS may also have an operator interface (functional units shown dashed in FIG. 2) which, for example, comprises an input device EE designed as a keyboard, an indicator device AE designed as a display, a speech/listening device SHE designed as a handset with a microphone MIF and a listening capsule HK, as well as a bell TRK.
The mobile part MT has the operator interface which may be used as an option for the base station BS, with the control elements described above associated with this operator interface.
Based on the document xe2x80x9cNachrichtentechnik Elektronik 42xe2x80x9d (Electronic telecommunications 42) (1992) January/February, No. 1, Berlin, DE; U. Pilger: xe2x80x9cStruktur des DECT-Standardsxe2x80x9d (xe2x80x9cStructure of the DECT Standardxe2x80x9d), pages 23 to 29 in conjunction with ETS 300 175-1 . . . 9, October 1992xe2x80x9d, FIG. 3 shows the TDMA structure of the DECT/GAP system TKS according to FIG. 1. In terms of the multiple access methods, the DECT/GAP system is a hybrid system in which radio messages can be transmitted in a predetermined time sequence from the base station BS to the mobile part MT and from the mobile part MT to the base station BS using the FDMA principle at ten frequencies in the frequency band between 1.88 and 1.9 GHz and using the TDMA principle according to FIG. 3 (Time Division Duplex operation). The time sequence is in this case governed by a multi-time frame MZR which occurs every 160 ms and has 16 time frames ZR each with a time duration of 10 ms. Information which relates to a C, M, N, P, Q channel defined in the DECT Standard is transmitted separately to the base station BS and the mobile part MT in these time frames ZR. If information for a number of these channels is transmitted in a time frame ZR, then the transmission takes place in accordance with a priority list where M greater than C greater than N and P greater than N. Each of the 16 time frames ZR in the multi-time frame MZR is in turn split into 24 time slots ZS each having a time duration of 417 xcexcs, of which 12 time slots ZS (time slots 0 . . . 11) are allocated to the transmission direction xe2x80x9cbase station BSxe2x86x92mobile part MTxe2x80x9d and a further 12 time slots ZS (time slots 12 . . . 23) are allocated to the transmission direction xe2x80x9cmobile part MTxe2x86x92base station BSxe2x80x9d. Information with a bit length of 480 bits is transmitted in each of these time slots ZS, in accordance with the DECT Standard. Of these 480 bits, 32 bits are transmitted as synchronization information in a SYNC field and 388 bits as wanted information in a D field. The remaining 60 bits are transmitted as additional information in a Z field and as protection information in a xe2x80x9cGuard Timexe2x80x9d field. The 388 bits which are transmitted as wanted information in the D field are in turn split into a 64-bit long A field, a 320-bit long B field and a 4-bit long xe2x80x9cX-CRCxe2x80x9d word. The 64-bit long A field is composed of an 8-bit long data header, a 40-bit long data record with data for the C, Q, M, N, P channels and a 16-bit long xe2x80x9cA-CRCxe2x80x9d word.
On the basis of PCT Reference WO94/10811 (Patent Claims 1 and 2), it is possible for the base station BS and/or the mobile part MS according to FIGS. 1 to 3 to have a radio part which is able to carry out either a fast channel change or a slow channel change. The terms used in these cases are a xe2x80x9cFast Hoppingxe2x80x9d radio part (FH radio part) and a xe2x80x9cSlow Hoppingxe2x80x9d radio part (SH radio part). In consequence, the base station BS is either an FH base station or an SH base station, and the mobile part is either an FH mobile part or an Sh mobile part.
Based on the DECT/GAP system according to FIG. 1, FIG. 4 shows a cellular DECT/GAP multi-system CMI (Cordless Multicell Integration), in which a number of the DECT/GAP systems TKS described above are present, each having a base station BS and one or more mobile parts MT concentratedxe2x80x94in the sense of a xe2x80x9chot spotsxe2x80x9d arrangementxe2x80x94at any given geographic location, for example in an administration building with large open-plan offices occupying whole floors. Instead of a xe2x80x9cclosedxe2x80x9d geographic location, such as the administration building, an xe2x80x9copenxe2x80x9d geographic location with strategic telecommunications significance is, alternatively, also possible, for example areas in cities with a high volume of traffic, a major agglomeration of commercial units and a large amount of movement by people, for the installation of a cellular DECT/GAP multi-system CMI. Some of the base stations BS arranged in the large office are, in contrast to the base stations shown in FIGS. 1 and 2, in this case designed in accordance with PCT Reference WO 94/10764 as antenna diversity base stations. The concentration of DECT/GAP systems TKS is in this case designed (gap-free radio coverage of the geographic location) such that individual DECT/GAP systems TKS operate in the same vicinity, with the cellular DECT/GAP radio areas FB overlapping.
The same vicinity can in this case mean, depending on the amount of overlapping, that
a) a first base station BS1 in a first telecommunications system TKS1 is arranged in a first radio area FB1 (radio cell), and a second base station BS2 in a second telecommunications system TKS2 is arranged in a second radio area FB2 (radio cell) and they can set up telecommunications links to at least one mobile part MT1,2,
b) a third base station BS3 in a third telecommunications system TKS3 and a fourth base station BS4 in a fourth telecommunications system TKS4 are arranged in a common, third radio area FB3 (radio cell) and can set up telecommunications links to at least one mobile part MT3,4.
In order to set up telecommunications links between the base station or stations BS and the mobile parts MT in DECT/GAP systems according to FIGS. 1 to 4, the base station BS (Radio Fixed Part RFP) transmits at regular time intervals via the DECT radio interface, and on simplex transmission paths, the so-called xe2x80x9cDummy Bearerxe2x80x9d (first information carrier), broadcast information which is received by the mobile part MT (Radio Portable Part RPP) according to FIGS. 1 to 4 and is used by it for synchronization and for setting up the link to the base station. The broadcast information need not necessarily be transmitted via the xe2x80x9cDummy Bearerxe2x80x9d.
It is also possible for no xe2x80x9cDummy Bearerxe2x80x9d to be required, because the base station already maintains at least one telecommunications link, the so-called xe2x80x9cTraffic Bearerxe2x80x9d (second information carrier) to another mobile part, on which it then transmits the necessary broadcast information. In this case, the mobile part which would like to have a telecommunications link to a base station can receive the broadcast information as if said broadcast information were transmitted via the xe2x80x9cDummy Bearerxe2x80x9d.
According to the ETSI publication ETS 300175-3, October 1992, Section 9.1.1.1, the broadcast information contains information about access rights, system information and paging information.
The system information furthermore contains additional information which informs the mobile part of the TDMA time slots which are available at the base station. In the DECT Standard (ETSI Publication ETS 300175-3, October 1992, Section 11.4.1, Note 4) and the GAP Standard which is a subset of the DECT Standard and has the task of ensuring interoperability of the DECT radio interface for telephone applications (see ETSI Publication prETS 300444, April 1995, Section 10.3.3), this additional information is called xe2x80x9cBlind Slotxe2x80x9d information or xe2x80x9cPoor Channelxe2x80x9d information. The transmission of the additional information is based on the xe2x80x9cBlind Slot Effectxe2x80x9d which occurs in TDMA/FDMA radio systems, like the DECT system. The xe2x80x9cBlind Slot Effectxe2x80x9d occurs in particular when
a) base stations according to FIG. 2 each have only one radio part with one transmitter and receiver and can thus transmit or receive on only one frequency during a time slot; if the base station maintains a duplex radio link in a specific pair of time slots, then it cannot set up any further radio links to other mobile parts in this pair of time slots;
b) base stations according to PCT Reference WO 94/10811 cannot transmit or receive in certain time slots because of technical restrictions (for example DECT base stations with a xe2x80x9cSlow Hoppingxe2x80x9d radio part).
Case b) is irrelevant in the following text since the present invention is based on base stations having a fast channel changing function (FH base stations).
Links are set up in accordance with the rules of channel selection (see ETSI Publication ETS 300175-3, October 1992, Section 11.4), according to which a new channel is selected for setting up a new link and the connection request (SETUP request) is transmitted. The channel selection is in this case carried out essentially in the central controller ZST of the mobile part MT or of the base station BS according to FIG. 2.
The xe2x80x9cBlind Slot Effectxe2x80x9d which has been explained above in the context of the base station BS also occurs, of course, in the mobile part MT; this arises, in particular, when
a) mobile parts according to FIG. 2 each have only one radio part with one transmitter and receiver and can thus transmit or receive at only one frequency during a time slot; if the mobile part maintains a duplex radio link to a base station in a specific pair of time slots, then it cannot set up any further radio links to another base station in this pair of time slots;
b) mobile parts according to PCT Reference WO 94/10811 cannot transmit or receive in certain time slots because of technical restrictions (for example DECT mobile parts with a xe2x80x9cSlow Hoppingxe2x80x9d radio part).
On the basis of the above statements and the fact that, on the one hand, xe2x80x9cFast Hoppingxe2x80x9d radio parts are considerably more complex to develop than xe2x80x9cSlow Hoppingxe2x80x9d radio parts and are thus more expensive and, on the other hand, there is interest in manufacturing the mobile parts as cost-effectively as possible, a scenario results in which the cellular DECT/GAP system according to FIG. 4 contains base stations with a fast channel changing function (Fh base stations) and mobile parts with a slow channel changing function (SH mobile parts).
In consequencexe2x80x94according to FIG. 5xe2x80x94such a system contains for example an SH mobile part (mobile part with a slow channel changing function) SH-MT1,2, which can be connected at the same time to two base stationsxe2x80x94an SH base station (base station with a slow channel changing function) SH-BS1 and an FH base station (base station with a fast channel changing function) FH-BS2 or two FH base stations (base stations with a fast channel changing function) FH-BS1, FH-BS2xe2x80x94by telecommunication. While the the SH mobile part SH-MT1,2 is connected to a first SH/FH base station SH-BS1, FH-BS1 by telecommunication, the SH mobile part SH-MT1,2xe2x80x94because it is located in the area where the radio areas FB1, FB2 overlapxe2x80x94could at the same time first of all set up, by synchronization, a telecommunications link in spe to a second FH base station FH-BS2 (keyword: roaming, handover). This synchronization is initiated by transmitting the broadcast information mentioned above from the respective base station to the relevant mobile part. The broadcast information can in this casexe2x80x94as already mentionedxe2x80x94be transmitted via a xe2x80x9cDummy Bearerxe2x80x9d or a xe2x80x9cTraffic Bearerxe2x80x9d. For reasons of spectral efficiency in DECT/GAP systems, not more than, for example, two TDMA time slots (transmission time slots for the respective base station) should be used for transmitting the broadcast information. This results in the following problem:
If, for example, the second FH base station FH-BS2 transmits the broadcast information via a xe2x80x9cDummy Bearerxe2x80x9d in the time slots xe2x80x9c3xe2x80x9d and xe2x80x9c5xe2x80x9d (for example the first xe2x80x9cDummy Bearerxe2x80x9d DB1 in time slot xe2x80x9c3xe2x80x9d and the second xe2x80x9cDummy Bearerxe2x80x9d DB2 in time slot xe2x80x9c5xe2x80x9d) to the SH mobile part SH-MT1,2, and if this SH mobile part SH-MT1,2 at the same time uses a xe2x80x9cTraffic Bearerxe2x80x9d TB to maintain a telecommunications link to the first SH/FH base station SH-BS1, FH-BS1 in the time slot xe2x80x9c4xe2x80x9d, then the SH mobile part SH-MT1,2xe2x80x94as a result of the fact that, because of the SH radio part, it cannot change from an active time slot to adjacent time slots when a frequency change takes placexe2x80x94cannot receive the broadcast information transmitted from the second FH base station FH-BS2 (xe2x80x9cBlind Slotsxe2x80x9d Effect).
FIG. 6 uses a time slot allocation table to show that the SH mobile part SH-MT1,2 is xe2x80x9cblindxe2x80x9d for signals which the second FH base station FH-BS2 transmits in the time slots xe2x80x9c3xe2x80x9d to xe2x80x9c5xe2x80x9d. Because of the xe2x80x9cTraffic Bearerxe2x80x9d TB, the SH mobile part SH-MT1,2 cannot receive anything in the time slot xe2x80x9c4xe2x80x9d and, because of the SH radio part, the SH mobile part SH-MT1,2 cannot receive the xe2x80x9cDummy Bearersxe2x80x9d DB1, DB2 in the time slots xe2x80x9c3xe2x80x9d and xe2x80x9c5xe2x80x9d.
The object on which the invention is based is to make it possible for a mobile part with a slow channel changing function to be synchronized in a manner which is economic in terms of frequencies and, at the same time, to at least two base stationsxe2x80x94for example to two base stations having a fast channel changing functionxe2x80x94in a cellular TDMA/FDMA radio system, in particular a cellular DECT/GAP system.
In general terms the present invention is a base station having a fast channel changing function in a cellular TDMA/FDMA radio system, in particular in a cellular DECT/GAP system. At least one base station having a fast channel changing function is arranged in radio cells of the cellular TDMA/FDMA radio system. A first radio module can be switched to any frequency of the TDMA/FDMA radio system. The base station can be connected by telecommunication to a mobile part having a slow channel changing function of the TDMA/FDMA. The base station emits information carriers. In order to receive the information carriers, the mobile part has a second radio module which includes a receive separation which occupies a first number xe2x80x9cnxe2x80x9d of TDMA time slots where xe2x80x9cnxe2x89xa72xe2x80x9d. A means for forming a pair of information carriers has a first information carrier and/or a second information carrier. These are designed such that a transmit separation, which occupies a second number xe2x80x9cmxe2x80x9d of TDMA time slots, between the two information carriers of the pair of information carriers is greater than the receive separation of the second radio module. The means are connected to the first radio module in order to transmit the pair of information carriers.
Advantageous developments of the present invention are as follows.
The transmit separation between the two information carriers of the pair of information carriers occupies three TDMA time slots. The receive separation between the two information carriers of the pair of information carriers occupies two TDMA time slots.
The mobile part which can be connected to the base station by telecommunication, is located in a region where the radio cells overlap or intersect.
The first information carrier is a xe2x80x9cDummy Bearerxe2x80x9d.
The second information carrier is a xe2x80x9cTraffic Bearerxe2x80x9d.
A DECT-specific base station in a DECT system, which base station can be connected to a DECT-specific mobile part by telecommunication.
The idea on which the invention is based is that a base station having a fast channel changing function in a cellular TDMA/FDMA radio system, in particular a cellular DECT/GAP system, transmits broadcast information to a mobile part having a slow channel changing function in the radio system, which already maintains a telecommunications link to another base station in the radio system, in a predetermined transmit separation which is defined as a number of TDMA time slots and is greater than a receive separation which is predetermined by a slow channel changing function in the mobile part and is defined as a number of TDMA time slots.
The transmit separation is in this case preferably determined by a program module in the central controller of the base station.